1. Field of the Invention
This invention relates generally to electronic equipment, such as computers, and, more particularly, to apparatus and methods for reducing electromagnetic interference caused by integrated circuit devices.
2. Description of the Relevant Art
Many electronic devices such as integrated circuits generate undesirable amounts of electromagnetic interference (EMI) during operation. For example, processors mounted on printed circuit boards (PCBs) may cause electromagnetic radiated emissions by injecting high frequency current into the printed circuit board, which then couples, directly or indirectly, to neighboring integrated circuits and other components. Such coupling may interfere with the individual performance of the devices, and thus adversely affect the overall performance of the system. In addition, because of the negative effects of EMI, the level of acceptable radiated emissions is subject to strict regulatory limits. For these reasons, it is desirable to contain or suppress the EMI generated by an integrated circuit.
There are two major methods by which integrated circuits can produce radiation: heatsink coupling and power bus injection. Various components have been employed to mitigate one or both of these EMI coupling mechanisms in a system. Some solutions involve grounding a lid or heatsink on the component and/or building a Faraday cage around the EMI producing chip (e.g., a CPU). In addition, various components such as gaskets, skirts, panels, and doors may be included in a system to contain emissions. Such components represent an additional cost and potential point of failure, as they typically require a separate part that must be added to the printed circuit board or enclosure.
In some systems containing processors, the second harmonic of the processor operating frequency may be a significant contributor to EMI. The EMI effects may be a result of high frequency current generated by complementary metal-oxide semiconductor (CMOS) devices in the integrated circuit. As integrated circuit technology advances, processors operate at increased frequency and power, thus presenting even greater challenges in maintaining emissions within acceptable levels.